FIGS. 1 to 3 schematically show a folding manner of a current foldable display device. As shown in FIGS. 1 to 3, a flexible screen 12 is fixed on two support plates 11a and 11b. The support plate 11a and the support plate 11b are connected by a rotating shaft 13. In order to achieve the folded and unfolded states, the support plate 11a and the support plate 11b can rotate about the rotating shaft 13.
The inventor has found that the foldable display device in the prior art has at least the following problems.
1. When the support plate 11a and the support plate 11b rotate about the rotating shaft 13, the flexible screen 12 is subjected to a tensile force due to a difference between rotation radius of the support plate 11a and the support plate 11b and the rotation radius of the flexible screen 12.
2. A gap G between the support plate 11a and the support plate 11b is fixed. When the gap G is excessively small, the flexible screen 12 in the folded state is subjected to a relatively large tensile force; and when the gap G is excessively large, the flexible screen 12 in the folded state cannot completely come into contact with the supporting plate 11a and the supporting plate 11b. 
3. After the foldable display device has been used for a while, the flexible screen 12 may not be flat in the unfolded state since the gap G between the support plate 11a and the support plate 11b is fixed.